fix: bad cacheing behaviour

src/net/torvald/terrarum/audio/MixerTrackProcessor.kt

@@ -210,7 +210,9 @@ class MixerTrackProcessor(bufferSize: Int, val rate: Int, val track: TerrarumAud
                     allocateStreamBuf(track)
                 }
 
-                streamBuf!!.fetchBytes()
+                if (track.currentTrack == null) throw IllegalStateException("Track ${track.name} is playing but also has null music track")
+
+                streamBuf?.fetchBytes() ?: throw NullPointerException("Null StreamBuf for ${track.name}")
             }
 
             var samplesL1: FloatArray

src/net/torvald/terrarum/audio/MusicCache.kt

@@ -8,11 +8,11 @@ class MusicCache(val trackName: String) : Disposable {
     private val cache = HashMap<String, MusicContainer>()
 
     fun getOrPut(music: MusicContainer?): MusicContainer? {
-        if (music != null && music.toRAM) { // for now only the on-the-RAM tracks are getting cached
-            println("Cacheing music ${music.name} for track $trackName")
+        if (music != null && !music.toRAM)
+            return music
+        if (music != null && music.toRAM) // for now only the on-the-RAM tracks are getting cached
             return cache.getOrPut(music.name) { music.makeCopy() }
-        }
-        else return null
+        return null
     }
 
     override fun dispose() {

src/net/torvald/terrarum/audio/TerrarumAudioMixerTrack.kt

@@ -44,12 +44,18 @@ class TerrarumAudioMixerTrack(
 
     var currentTrack: MusicContainer? = null
         set(value) {
-            field = musicCache.getOrPut(value)
+            field = if (value == null)
+                null
+            else
+                musicCache.getOrPut(value)
         }
 
     var nextTrack: MusicContainer? = null
         set(value) {
-            field = musicCache.getOrPut(value)
+            field = if (value == null)
+                null
+            else
+                musicCache.getOrPut(value)
         }
 
     var volume: TrackVolume = 1.0